What defines an oxygen-deficient atmosphere?

What defines an oxygen-deficient atmosphere?

• A. an area with less than 19.5% oxygen
• B. an area with more than 19.5% oxygen
• C. an area with exactly 21% oxygen
• D. an area with any oxygen level above 0%

Answer: (A)

An oxygen-deficient atmosphere means there isn’t enough oxygen to support normal human respiration. Safety standards define this as less than 19.5% oxygen by volume. Normal air is around 20.9–21% oxygen, so dropping below 19.5% can cause dizziness, headaches, impaired judgment, and eventually fainting or unconsciousness. That’s why the correct description is a region with less than 19.5% oxygen. The other statements describe normal or higher-than-normal oxygen levels, which do not indicate deficiency.

An oxygen-deficient atmosphere means there isn’t enough oxygen to support normal human respiration. Safety standards define this as less than 19.5% oxygen by volume. Normal air is around 20.9–21% oxygen, so dropping below 19.5% can cause dizziness, headaches, impaired judgment, and eventually fainting or unconsciousness. That’s why the correct description is a region with less than 19.5% oxygen. The other statements describe normal or higher-than-normal oxygen levels, which do not indicate deficiency.